Flour and Milk Frosting: Smooth, Not-Too-Sweet Buttercream

Flour and milk frosting, often called ermine frosting, is a silky buttercream made by cooking flour, milk, and sugar into a thick paste, then whipping it with butter and vanilla. It is smooth, creamy, and less sweet-tasting than many frostings made with powdered sugar, making it a lovely choice for cakes and cupcakes.

Ingredients

1 cup (240 ml) whole milk
1/4 cup (31 g) all-purpose flour
1 cup (200 g) granulated sugar
1 cup (226 g) unsalted butter, softened but still cool
2 teaspoons (10 ml) vanilla extract
1/8 teaspoon (about 0.7 g) fine salt

Whole milk gives the cooked base a rich, creamy texture. Two-percent milk also works, though the finished frosting may be a little less rich. Use unsalted butter so you can control the salt; if you only have salted butter, omit the measured salt. The flour is cooked with the milk before it goes into the frosting, so it should not taste raw.

Instructions

Whisk the base ingredients together. In a small, heavy saucepan, whisk the flour and granulated sugar until no obvious flour clumps remain. Gradually whisk in the milk, scraping the corners and bottom of the pan as you go. Starting with a smooth mixture helps prevent lumps during cooking.
Cook until thick. Set the pan over medium heat and cook for about 6 to 8 minutes, whisking constantly. At first the mixture will be thin; as it heats, it will thicken into a smooth paste, similar to thick pudding. Once it bubbles gently and holds a line briefly when you draw the whisk through it, cook for about 30 seconds more, then remove it from the heat. Do not leave it unattended: the base can scorch on the bottom or form lumps if it is not stirred.
Cool the cooked base completely. Scrape the paste into a shallow bowl and press a piece of plastic wrap directly onto its surface to prevent a skin from forming. Let it cool at room temperature for 45 minutes, until it is no longer warm. The butter and cooked base should be close to the same temperature before mixing; a warm base can melt the butter, while a cold base can make the frosting look curdled.
Whip the butter. When the base is cool, place the softened butter in a large bowl. Beat with a hand mixer or stand mixer fitted with the paddle attachment for about 3 minutes, stopping once or twice to scrape the bowl. The butter should look pale, fluffy, and creamy, with no hard cold pieces. Add the vanilla and salt and beat briefly to combine.
Add the cooked base gradually. Beat in the cooled paste one tablespoon at a time, letting each addition blend in before adding the next. Scrape the bowl and beater, then beat for another 2 to 3 minutes until the frosting looks light, smooth, and uniform. If it appears slightly separated at first, continue beating; it often comes together as the ingredients combine.
Use or chill the frosting. Spread or pipe the frosting onto completely cooled cake or cupcakes. This batch makes enough for a moderate layer of frosting on about 12 cupcakes, or a filling and thin coating for a two-layer 8-inch cake. For generous piping or a thickly frosted cake, make one and a half or two batches.

Tips

Keep whisking over the heat. Constant stirring is the simplest way to keep the flour mixture smooth and stop it sticking to the pan. If a few small lumps appear, whisk briskly; if necessary, press the cooked base through a fine-mesh sieve while it is still warm.
Match the temperatures. The butter should be pliable but not shiny or melting, and the cooked base should be fully cool. If the base is still warm, wait before mixing. If the finished frosting looks curdled, keep beating for a few minutes; if it is very soft, chill it for 10 to 15 minutes and beat again.
Measure flour accurately. Spoon flour into a dry measuring cup and level it rather than scooping and packing it. Too much flour can make the cooked base pasty and the frosting heavy. A kitchen scale gives the most reliable result.
Choose the right milk and butter. Whole milk and unsalted butter give a full, rounded flavor, but 2-percent milk is a workable substitute. Avoid margarine or spreadable tub butter, which can contain more water and may leave the frosting softer or less stable.

Serving Suggestions

Use this frosting on vanilla, chocolate, spice, or red velvet cake, where its mild sweetness complements the cake without covering up its flavor. It also works well between cake layers, on cupcakes, or spread over a simple sheet cake. For the neatest finish, frost only after the cake has cooled completely; even a slightly warm cake can soften the butter and make the surface slide.

The texture is soft and easy to spread at a cool room temperature. If you plan to pipe defined swirls, chill the frosting briefly until it holds its shape, then give it a quick stir or short rewhip before filling a piping bag. Bring a chilled frosted cake out shortly before serving so the frosting can soften enough to slice cleanly.

Variations

Chocolate: Beat 2 ounces (57 g) of cooled, melted semisweet chocolate into the whipped butter before adding the cooked base. Let the chocolate cool until fluid but not warm; warm chocolate can soften the butter. The result is a mild chocolate frosting rather than a very dark, intensely sweet one.

Citrus: Replace the vanilla with 1 teaspoon (5 ml) vanilla plus 1 teaspoon (5 ml) finely grated lemon or orange zest. Zest only the colored outer peel, not the bitter white pith. A little citrus juice can also be added, but use it sparingly so the frosting does not become loose.

Coffee: Dissolve 1 teaspoon (2 g) instant espresso powder in 1 teaspoon (5 ml) hot water, cool it, and beat it in with the vanilla. This gives a gentle coffee note; add more a little at a time if you want a stronger flavor, checking that the frosting stays thick enough to spread.

Less dairy-rich: You can use 2-percent milk in place of whole milk, but the result will be slightly less rich. Plant-based milk may work, especially an unsweetened, unflavored variety, though brands differ in thickness and flavor. The cooked base may set a little differently, so judge it by the thick-pudding texture rather than the exact minute on the clock.

Storage and Reheating

Because this frosting contains milk and butter, refrigerate it in an airtight container within 2 hours of making it or serving it. It keeps well in the refrigerator for up to 4 days. If it is already on a cake, cover the cake and refrigerate it; allow it to soften at room temperature before serving, while keeping total time at room temperature under 2 hours.

For longer storage, freeze the frosting in a sealed freezer-safe container for up to 2 months for best quality. Thaw it overnight in the refrigerator, then let it stand until cool and pliable. Beat it for 2 to 4 minutes to restore a smooth texture. This frosting does not need reheating; direct heat can melt the butter and make it greasy. If it seems too soft after thawing, chill it briefly and whip again.

If the frosting has been left out for more than 2 hours, discard it rather than saving it for later. In a warm room or outdoors in hot weather, shorten that window, since butter-based frosting softens quickly and the milk-based cooked base is perishable.

Frequently Asked Questions

Why is my flour and milk frosting lumpy?
Most lumps form when flour is not whisked smoothly into the milk or the mixture is not stirred steadily as it heats. Whisk the flour and sugar together first, add the milk gradually, and keep whisking over medium heat. If the cooked base still has a few lumps, strain it while warm before cooling it.

Can I make the cooked flour-and-milk base ahead?
Yes. Cook it, press plastic wrap directly onto the surface, and refrigerate it for up to 2 days. Before mixing, bring it toward room temperature so it is not cold and firm. The butter and base blend most smoothly when they are at similar temperatures.

Why does the frosting look curdled or runny?
A temperature mismatch is usually the cause. If the base was too cold, the butter can firm into small flecks; keep beating, or warm the outside of the bowl very briefly with your hands before continuing. If the base was warm, the butter may have softened too much. Chill the bowl for 10 to 15 minutes, then beat again until the frosting holds its shape.

Does this frosting taste like flour?
It should not. Cooking the flour and milk until the mixture is thick and gently bubbling removes the raw-flour taste. If you notice a starchy flavor, the base may have needed more cooking, or the flour-to-milk ratio may have been off. Keep the whisk moving and cook until the paste is thick before cooling it.

Can I use powdered sugar instead of granulated sugar?
Granulated sugar is used here because it dissolves into the milk-and-flour base as it cooks. Powdered sugar contains starch and can change the consistency, so it is not a direct one-for-one substitute in this method. For the smoothest result, use granulated sugar and whisk the base until it is fully thickened.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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